Amber Frey on Peterson: 'Justice Was Served'

Scott Peterson's mistress, Amber Frey, has spoken for the first time since her ex-lover's Dec. 14 sentence for murdering his pregnant wife Laci, telling NBC's Matt Lauer that she believes "justice was served."

The interview, which will air on Today and Dateline NBC next Monday and Tuesday, coincides with the release of her book Witness: For the Prosecution of Scott Peterson, excerpts of which appear in the latest issue of PEOPLE. In it, she talks about her initial affair with Peterson, the unraveling of his lies and her tearful meeting with Laci's family after going public about her affair with the fertilizer salesman.

The massage therapist tells Lauer, however, that she didn't think Peterson, 32, should have received the death penalty.

"I felt life (in prison) gives him every day to live with what has happened," she says, according to the New York Post and Daily News. "It's almost to me death is so much simpler. ... You know that he doesn't have to live with that every day."

She also says of her onetime lover: "There isn't any truth that comes out of this man's mouth. I just saw him as this compulsive liar ... a pathological liar."

During the police investigation into the disappearance of Laci Peterson in late 2002, Frey agreed to tape phone conversations with Scot that were later played in court – revealing his layer of lies.

Frey tells Lauer that her "stomach was turning" as she awaited Peterson's calls. "I was shaking," she says. "My hands were just sweaty."

As for facing Peterson in the courtroom, where she testified, Frey remembers: "I was asked to look and identify him. And in my mind, I knew he was there. But I was there for a reason, and I didn't allow his presence there to affect what I needed to do."

In the book, Frey also details her meeting with Laci's family. "It took a huge weight off my shoulders, just knowing that they knew that I wasn't the enemy," she writes. "But in another way, that visit broke my heart. When I looked into the eyes of the people who knew Laci best, I saw something I didn't want to see: a group of people who desperately loved Laci, and who were beginning to suspect she wasn't coming home."

For more from Frey's book, pick up the latest issue of PEOPLE, on newsstands Friday.